1. Field of the Invention
The present invention relates to an equivalent circuit for a coil incorporated in a circuit simulator used for analysis of electrical equipments including an electric motor and a generator, etc., a circuit simulator and a method of preparing the same, and a storage medium for storing a program for realizing the circuit simulator. In particular, the present invention relates to arts for determining the equivalent circuit for a coil being a magnetic circuit in an electrical equipment in order to make a model for analysis by a circuit simulator closer to an actual coil, and arts for improving the performance and practicality of commercially available ordinary circuit simulator programs.
2. Description of the Related Art
When a household electric appliance manufacturer or auto maker, etc. uses, for example, an electric motor in a product, it generally conducts a detailed study of operating characteristics in electrical circuits of the electric motor using a circuit simulator before producing an actual motor. In this case, the circuit simulator treats the electric motor as a device comprised of electrical elements included in the mechanical structural parts and a control circuit for controlling the supply of power to the mechanical structural parts. When the circuit simulator performs calculations for an electric motor, it expresses the electric motor as an electrical equivalent circuit and usually uses electrical elements of the electric motor in the circuit simulator.
The above-mentioned circuit simulator is realized by running a simulation program simulating the configuration and operation of the electrical circuit equivalent to the electric motor on a computer. The operator at the user installs, starts up, and runs the simulation program in the computer, views the state of the electrical equivalent circuit displayed on the screen of the display of the computer, and simulates the operation of the electric motor through the electrical equivalent circuit. The circuit simulator to be used is generally provided by commercially available software. As the circuit simulator, for example, PSIM (made by Powersim Inc.), Matlab®/Simulink® (made by The MathWorks Inc.), and other products are being sold.
The conventional commercially available circuit simulators can set several electrical characteristics for the motor elements. A circuit simulation enables the calculations of the electrical circuit to be matched with the actually measured values to thereby evaluate the performance of a product without manufacturing a trial product. This enables advance evaluation of the performance of the electrical circuit and enables evaluation of the performance by a short calculation time and faster cycle.
However, in the conventional circuit simulator, the set values of the electrical characteristics are constant values based on lumped constants and cannot be changed during the computer simulation. In an actual electric motor, however, the values of the inductance and other electrical characteristics of the motor elements change with each instant. For this reason, the problem has been pointed out that a separation occurs between the results of calculation by the conventional circuit simulator and the actually measured values in actual devices, and the accuracy of calculation is poor.
As a means for solving the above conventional problem, the method has been proposed of analyzing the electrical characteristics of an electric motor in advance utilizing the finite element method (electromagnetic field analysis) so as to obtain data on the constantly changing values of the electrical characteristics of the electric motor and connecting the data of the values of the electrical characteristics to the circuit simulator (Japanese Patent Publication (A) No. 2003-75521 and Japanese Patent Publication (A) No. 2003-85218). Explaining this more specifically, the practice has been to extract the values of the electrical characteristics of the electric motor in accordance with specific situations based on the finite element method, prepare a data base of the values of the electrical characteristics, and have the circuit simulator run calculations while referring to the data base.
Magnetic field analysis based on the finite element method enables analysis of the characteristics of the mechanical structural parts of the electric motor as they stand, but tremendous time is taken if finding them directly linked with the electrical circuit.
Further, when connecting magnetic field analysis by the finite element method and the circuit simulator, as explained above, there is the problem that the work of extracting the data of the electrical characteristics in advance is required. Further, while a data base of the electrical characteristics is prepared, the data base has nonlinearity, so iterative calculation by the circuit simulator is necessary. Therefore, when it is not possible to run nonlinear iterative calculations on the circuit simulator, data of nonlinear characteristics cannot be handled.
Ordinarily, the only variable circuit elements which a conventional commercially available circuit simulator provides the user are the current source and voltage source. There are no variable inductance elements etc. However, the actual characteristics of a coil forming a magnetic circuit handled in an electric motor or other electrical devices or equipments are not constant values, but variable values, so some sort of modelization is necessary for inherently variable inductance elements to be handled by a circuit simulator.
Further, the circuit simulator of an electrical device having three coils connected by a Y-configuration (star configuration) or a delta configuration inherently functions as an electric motor or functions as a generator in accordance with the relative magnitude of the power supplied from the outside and the power generated at the coil side. For this reason, when using the above circuit simulator for analysis, setting the analysis conditions of the model so as to select between simulation and analysis as an electric motor or simulation and analysis as a generator becomes extremely important. From this viewpoint, provision of a circuit simulator enabling the analysis conditions to be suitably set has been desired.